A photographic apparatus has heretofore been developed for obtaining a record of the interior condition of a pipeline and has been found to be highly advantageous, especially in connection with the testing of pipelines used for transporting natural gas in its raw state. Natural gas may contain coarse solids, plus other gases and liquids which may combine to form corrosives. For example, the gas may include a combination of carbon dioxide and free water which is operative to produce carbonic acid and to corrode steel. The corrosive effect can be augmented by an erosion effect when the rate of flow is high and at bends and overweld beads or the like where the flow is turbulent.
Such corrosion and erosion as well as other defects can eventually lead to complete failure of the pipe but if detected at an early time, it is possible to effect repair or to otherwise take corrective measures. For example, it is possible to move devices known as "pigs" through a pipe and by moving a series of such pigs through a pipe, it can be cleaned, etched, washed, dehydrated and then coated with a protective coating such as an epoxy.
In the apparatus heretofore developed, an image is projected to a film plane from an illuminated internal surface area of the pipe along a viewing axis which is normal to the axis of the pipe, a generally rectangular image being produced in the film plane which corresponds to a generally rectangular internal surface area of the pipe. It is possible to obtain a photographic record which can be accurately interpreted and which indicates when repair or maintenance procedures are necessary. Preferably, the camera and associated illumination means are located within a chamber between forward and rearward cup assemblies in a device which is moved through the pipeline by the pressure of fluid within the pipeline.
Another feature of the device as heretofore developed is in the provision of weight means such that the orientation of the viewing axis may be fixed relative to a vertical position. Normally, it is desirable to place the viewing axis at a "six o'clock" position because it is found that the areas of primary interest are those in the lower side of the pipe where water might accumulate to lead to corrosion of the pipe.
The device as heretofore developed has produced highly satisfactory results in a number of testing operations but has had limitations with respect to testing of pipelines in which there is an excessive amount of water or in which conditions are otherwise adverse. The accumulation of moisture in a liquid form in the lower side of the pipeline is particularly troublesome in that it may obscure the images of corrosion or other defects of the pipeline. In some cases, moisture may be carried in the gaseous medium in the pipeline to cause a fog effect. Both of such conditions are such that they may sometimes escape detection in the photographs themselves, being sometimes operative to develop photographs of a generally uniform nature which are similar to those produced when the surface within the pipeline is smooth with no defects therein.